IL25176A - Solvent extraction method for removing salt from water - Google Patents

Description

HltHl |Π3 ΤΝΠΓ'Ί Π ' D 1 Q 3 ' 3 "Π U PATENTS AND DESIGNS ORDINANCE SPECIFICATION Solvent extraction method for removing salt from water j (we) Ralph W. Buetow. a citizen of the U.S.A., of 1330 Shird Street, Wausau, Wisconsin, U.S.A. do hereoy declare the nature of this invention and in what manner the same is to " e performed, to particularly described and ascertained in and by tY following statement: - SOJLVENS--EXTRACTION-MSTHOIX-E R--BEMOVINO-SALT -WATER the Fresh water is produced from sea water by/solvent extraction process of this invention. Solvents utilized in the process render the vater produced potable and suitable for human consumption or agricultural use, and extraction temperatures are near ambient ocean temperature to provide fresh water more economically than is provided by either evaporation or freezing processes. Water of saline concentration equal to that of any of the worlds oceans can be used in the process rendering the process more utilitarian than electro-dialysis, ion exchange or semi-permeable membrane filtration processes v/hich can be utilized for producing fresh water only from water having lower saline content than that of sea water. A plant for the practice of this invention can be of any size to one capable ofjproducing millions of gallons of fresh water daily and can be economically situated in proximate relation to the world's major population centers or potentially arable desert land adjacent to the world's oceans.

The process is accomplished by first Introducing an cyclic solvent, as hereina ter defined Into sea water, either chemical with or without additional introduction of another/agent which may preferably be a small quantity of a condenslble gas, to cause two saline liquid phases of differing salinity to form or to precipitate a solid salt phase, and then separating phases and treating liquid phases for recovery of solvent by adding either an azeotroplc distillation solven and distilling the azeotrope or preferably by adding a second extraction solvent, preferable a larger quantity of a condenslble gas, causing for-mation of a saline phase and a non-saline phase, after separathe tion of which phases condenslble gas can be expelled by heating pressure reduction, all with an object to providing a more economical method than i3 presently known for converting sea water to fresh water suitable for large scale agricultural, industrial, and potable water use and consumption.

The invention is illustrated b the accompanying drawings in which: Figure 1 is a schematic flow diagram of the process of this invention.

Figure 2 is a solvent crystallization diagram or s-trioxane.

In solvent-solvent extraction procedure phases ormed by introduction of a first solvent in an extraction vessel are withdrawn as two component streams, as herein one comprising water having not more than about 0.03 percent by weight residual salt, and the other comprising concentrated brine, if multiple extraction procedure using sea water is employed, with separation of solvent from the streams being subsequently accomplished by introducing into a stream a second solvent which herein is preferably a condensed gas to render water and the first solvent substantially immiscible or to render an azeotrope to form with azeotropic distillation being made possible.

Solvents suitable for use in this invention to effect initial separation of saline phases from sea water are those having mutual dual solubility relationships with saline water wherein large differences in salinity occur between solution phases; oxa-cyclic compounds such as dioxane, or CH2-0-CH2-0H2-GH2-0, s-trioxane, GH2-0-CH2-0-CH2-0, trioxepane, i I- i GH2-CH2-0-CH2-0-CH2-0, tetraoxocane, CH2-0-GH2-0-C¾2-0-CH2-0 and homologs and lower alkyl substituted derivatives and alkoxy substituted derivatives thereof are suitable, the more preferred solvents having combined properties of low-toxicity, high stabili ty under vaporizing temperatures and pressure conditions, low hydrolysis constant, and non-corrosive activity so that the end uses for which product water is suitable are not restricted* s-frioxane (i.e. symmetric? unsymmetric molecular structure of is not recorded in chemical literature) is a preferred sol vent for use herein alone and in synergistic combination with a minor proportion of trioxepane (described in U.S. Patents 2,475,610 and 2,625,569). s-frioxane melts at 61°C, has a of water solution at 25°C. to total miscibiltty in hot water, vaporizes under atmospheric pressure at 115°C shows no measurable decomposition at 200°C. for 2 hours, is not hydrolyzed in we k acid solution, and is of very low toxicity.

At atmospheric pressure s-trioxane of concentrations above about five (5¾) weight percent will crystallize from aqueous solution at about 48°C. and distill as a constant boiling mixture of about 70 percent s-trioxane and 30 percent water at about 91°C.; addition of another solvent as agent may effect lowering of crystallization temperature and distillation temperature, e.g. at atmospheric pressure with carbon dioxide added crystallization temperature may be lowered to 30°C. or below and with hexane added distillation temperature may be lowered 3 is at to about 70"C. ^-jirioxane/^stable and usable herein pressures of from sub-atmospheric to 70 atmospheres or more.

Recovery of solvent used to separate saline phases from water solution may be effected by a second solvent extraction using a non-polar water immisAble solvent, for example, ethylene dichloride or methylene chloride, or may be effected using a condensed gae such as for example nitrous oxide, carbon dioxide, or sulfur dioxide, or may be effected by azeotroplc distillation, for example with hexane added to reduce distillation temperature.

Oxa-cyclic compounds, i.e. compounds of closed ring structure comprising multiple ( -C-0-C ) bonding, are preferred for use herein as solvents to effect separation of saline phases to those of acyclic structure because it is believed that hydrogen bonding of water is promoted by ether linkages and in a cyclic molecule structure hydrogen bonding is essentially internally complete so that cross bonded aggregations of molecules or polymers is substantially avoided; the sterlc configuration of s-trioxane wherein oxygen atoms and carbon atoms are grouped mutually independently in non-intersecting planes is believed to particularly enhance internal hydrogen bonding.

Dissolved mineral salt concentration in the solvent rich phase of s-trioxane-water solutions of this invention at 48°C. may be about 1.6 percent by weight maximum calculated as sodium chloride in water; at lower temperature s-trioxane crystalliza condensable gas agent such as carbon dioxide will reduce sodium chloride solubility therein to 0.1 percent by weight calculatecj^ as sodium chloride in water or the solvent rich phase in comparison to 1.6 percent solubility in water without such addition, and further s-trioxane precipitation temperature in the phase is reduced to about 30°C. After separation of the saline phases solvent recovery may preferably be effected by a second extraction such as extraction with condensable gas, e.g. carbon dioxide. Addition of the order of about 50 weight percent in the solvent rich phase will substantially cause solvent ani water immlsci-bility and separation into two phases with residual contamination of the water by the solvent being under 0.03 percent by weight and within tolerable limits for human consumption and for agriculture and industrial use, the condensable gas, e.g. carbon dioxide being recoverable after separation of solvent and water by slight heating and/or release of pressure. The process of this invention may be performed throughout at near ambient temperature, i.e. between about 15°C and 40°0 with super-atmospheric pressure being necessary only to confine gases and vapors, such as to contain carbon dioxide during extraction and to condense and recover it after it is freed from the product water. Uhe process of this invention may be conducted at pressures, either sub-atmospheric or super-atmospheric as ©ay be most advantageous in view of the particular conditions existing at a process installation. fieferring now to Figure 1 , a schematic flow diagram of a process of this invention is shown wherein salt feed water stream 10 is introduced into extraction tower 11. fhe tower may be heated or cooled by conventional means which are rot shown* but which may comprise internal heating or cooling coils, A temperature greater than the temperature at which crystallization of components would occur must be attained. Solvent is introduced into tower 11 through pipe 8, and an agent which can reduce the temperature at which freezing will occur, such as carbon dioxide, may be Introduced into either the solvent or feed water before entry into to¾er 11, or may be introduced directly through pipe 9 into tower 11 as shown. For use of s-trioxane as solvent and carbon dioxide as agent (in concentration fif j the order of about 10 weight percent of total solution) a temperature in tower 11 of 40°C. is sufficient to avoid precipitation of crystals of trioxane. Total vapor pressure of about 250Ϊ40 p.s.i. will obtain under such conditions. The contents of tower 11 are brought into intimate mutual contact by. means not shown, but which may comprise counter-current flow of components through sieve plates, tower packing or the like. Two phases form in tower 11 as well separated raf inate and extract layers. The upper phase (raffina e if the stated components are used) is pumped by. pump 12 to solvent recovery tower 22 through pipe 14. The lower phase (extract) is pumped from the bottom of tower 11 by pump 15 to second stage extraction tower 16 through pipe 17. Solvent is introduced into separating tower l6 through pipe 8', and/agent is added to the bottom of tower ΐβ, through pipe 9*. Raffinate and extract are pumped from tower 16, which may be similar in structure and operation to tower 11, through pumps 12» and 15' respectively. The raffinate is emptied to pipe 14 and the extract is conducted through pipe 178 to wash tower 20. The agent which is used to wash the water fraction is introduced to tower 20 through pipe 9". From tower 20, which may be similar in structure to towers 11 and 16, raffinate is pumped from the top of wash tower 20 by pump 12" to recovery tower 21 through pipe 14· and extract is pumped by pump 15" through pipe 14 to solvent recovery tower 22. In solvent recovery tower 21, which may be structurally similar to extraction towers 11, 16, and 20, a second solvent is introduced which in Figure 1 is the same material as the agent introduced into the extraction towers 11, 16, and 20; using the above stated components the second solvent is liquid carbon dioxide and is introduced tower 21 through pipe 9»»». The more dense solvent phase is withdrawn from tower 21 through pipe 25 to heater 26. The less dense heater 28 through pipe 29.

A second solvent is introduced into solvent recovery tower 22 in a manner similar to that shown for tower 21. In ible Figure 1* a co de s^ gas is used in different concentrations freezing depressant both as eefctv*fcfci*s/agent and separating agent to effect respectively mixing and de-mixing action on the mixture of solvent and water in the towers. The more dense solvent phase i3 withdrawn from tower 22, in all material respects similar to tower 21 , through pipe 3 into pipe 25 and heater 26. The less dense brine phase is pumped from the top of tower 22 by pump 31 through pipe 32 to heater 33. Each of heaters 26, 28, and 33 is heated, means not shown, to a temperature sufficiently great to vaporize the second solvent. The critical temperature of carbon dioxide is 31°C., and heating may not be necessary under all operating conditions.

The vapors released in heaters 26, 28, and 33 are piped (by pipe 35 for heater 26) into manifold 36 which exhausts in cooler 37 where the vapors are condensed and withdrawn by pipe 33 into liquid activating solvent make-up pipe 9· Cooler 37 may incorporate compressor stages or other means as may be necessary to condense, dry, and otherwise render the recovered solvent reusable. If the process is operated at super-atmospheric pressure, means not shown, such as brine and product water, driven turbines may be used to pump feed water into the process.

The brine discharge from the bottom of heater 33 may be collected for by-product recovery. Solvent discharge from heater 26 is returned through pipe 39 to solvent make-up pipe 8 for re-use. Fresh potable water is obtained from the bottom of heater 28 containing less than 0.05 weight percent salt and not more than about 0.03 weight percent solvent if trioxane is used.

In the process illustrated in Figure 1, i may be desirable to pre-mix and filter feed components before introducing them to extraction tower 11 to remove solid impurities and any complexion hydrate precipitate that may form upon addition of extraction solvents to saline viater although such precipitation is not substantial.

Figure 2 is a crystallization diagram for a system of xfater-s-trioxane-carbon dioxide in which the effect of small quantities of carbon dioxide in depressing the freezing point of s-trioxane in aqueous solution will be noted, i.e. the freezing point at atmospheric pressure is depressed from 8°C. to about 15°C. with addition of an amount to 50 weight percent liquid carbon dioxide. The critical temperature of carbon dioxide is 31°C., however, the solubility of carbon dioxide in s-trioxane is sufficiently great to enable it to be dissolved in water-s-trioxane solutions or mixtures in all feasible solvent proportions to about 20 weight percent of the maximum usable in tower 11 of Figure 1, or to about 50 weight percent as usable in the recovery towers.

As used herein "potable water" means water having less than 0.2 percent by weight mineral salt content; brackish water from about 0.2 percent to 0.5 percent by weight mineral salt content; sea water about 3.5 percent by weight mineral salt content; brine greater than about 3.5 percent by weight mineral salt content.

"Condensible gas" as used herein means either a substance which has a critical temperature at or above the range of temperatures useable in the process of this invention, or a gaseous substance which can be dissolved in solvents or water used in the process in amount to produce desired mixing or demixing effect of liquid phases. 25176/2 The following examples illustrate the process of this inventio : EXAMPLE 1 ml. Pacific Ocean water obtained near Los Angeles, California, having 3.4 wt. percent total halogen content calculated as HaCl and 60 gms. s-trioxane were placed in a separators funnel, heated in a water bath to 61°C and s tirred until complete dissolution occurred. The funnel and contents were cooled to 51°0 in the water bath with frequent stirring with the appearance of two phases, the lower phase bein 58 ml. in volume and the supernatant phase 19 ml. in volume. The phases were separated at 51°C after which the lower phase was cooled to below 48°C with the precipitation of s-trioxane crystals. An equal volume of ethylene dichloride was added to the lower phase dissolving all s-trioxane crystals and freeing occluded water which floated on a s-trioxane-diethylene dichloride rich lower layer. Samples of the floating water layer were removed by pipette and washed with ethylene dichloride to remove residual traces of s-trioxane after which they were titrated for chloride with 0.1 H AgNO^. The samples obtained analyzed 1.8 wt. percent total halogen calculated as EaCl.

EXAMPLE II 50 ml. of 3·5 wt. percent solution of NaCl in watei^and 121 gms. of s-trioxane were p¾ced in a 300 ml. separatory funnel at 61°C and completely dissolved with stirring into one phase. The total solution volume was 155 ml. The contents of the funnel were cooled in a water bath slowly with frequent 3tirring and were observed to separate were observeds at 57°C the lower phase 110 ml,; at 52°C 100 ml. I and at 48°C. s-trioxane crystallization occurred, The temperature of the funnel and contents wis raised to 57°C. by heating in a water bath with stirring. At 57°C. the lower phase of 110 ml. was removed to a second separatory funnel.

A volume of 40 ml. of the remaining upper layer was washed with an eq l volume of ethylene dichloride with the appearance of a brine layer floating on a s-trioxane-ethylene dichloride rieh lower layer. The lower layer was removed from the first funnel and the remaining brine layer in the funnel was again washed with ethylene dichloride to remove traces of s-trioxane. After removing the second ethylene dichloride wash layer the brine layer remaining, 21 ml. in volume, was titrated with 0.1 H AgNG^. It was found to contain 4.5 wt. percent NaCl. The temperature of the second funnel was adjusted to 55°C. Two layers appeared. The lower layer was removed and treated as in Example I. The supernatant layer was washed and analyzed in the manner of the supernatant layer of the first funnel. The brine layer, 11 ml. in volume, formed in the supernatant phase, 15 ml. In volume, from the second funnel contained 4,0 wt. percent NaCl, and the brine layer, 19 ml, in volume, formed in the lower phase, 95 ml. in volume, from the second funnel contained 1.7 wt. percent NaCl as titrated with 0.1 N NO^. 4itional extractions of 3.5 wt. percent HaCl solutions in water were separately conducted in the manner and with the proportions of Example II with each of the following solvents replact para-dioxane rimethyl trioxane (paraldehyde).

Product water of equivalent saline concentration in either case was substantially less than yield obtained in Example II, and in Example II. Solvents which may be preferred to both latter named solvents include 1,5,5 trioxepanej 1,3,5 s-trloxane, 2-oxy; 1,3,5 s-trioxane, 2*4,6 trioxy, and mono-methyl and mono-ethyl substituents of each of said solvents. Solvents may be used in combination with tetraoxocane (CH2-0-CH2-0-CH2-0-OH2-0) or lower alkyl derivatives. The stability of each said solvent was less at elevated temperatures and under hydroiyzing conditions than that for s-trioxane, and none is preferred to s-trioxane for use in the method disclosed herein.

Precipitation and separation of phases with s-trioxane conducted as in Example II, but at increasing pressures to 1500 p.s.i. did not materially affect phase volumes, and phase compositions were found to be similar to those of Example II in BaCl content.

The processes of this invention can be performed by continuous multiple extraction methods as illustrated by the following Example.

Example III 50 ml. of 3.5 wt. percent solution of NaCl in water and 1 0 gms. s-trioxane were used.

The precipitative extraction procedure of Example II was followed with additional extractions being made in the described manner of each lower phase of the second funnel and of the supernatant phase of the first funnel. 25176/2 Exanrole IV ml. of 3.5 wt. percent solution of NaCl in water and 60 gms. s-trioxane were placed in a separatory funnel at 54 C. and after stirring and dissolution were observed to separate into a supernatant phase 30 ml. in volume and a lower phase 50 ml. in volume. The procedure of Example II was followed by;! 'cooling the funnel and at 51°G. separating a lower phase 49 ml. in volume. s-Trioxane was extracted from the separate phases by double washing with ethylene dichloride in the manner of Example II to yield water layers 7 ml. in volume with 1.8 wt. percent NaCl in the lower phase and 16 ml. in volume with 4.6 wt. percent NaCl in the supernatant phase.

Example V 25176/2 56 gms. s-trioxane and gms. sea water having 3.4 percent by weight salt content calculated as NaCl were placed in a stainless steel separatory funnel and dissolved by being heated to 60°C. with stirring, after which the funnel was tightly sealed by securing the top; 6 ml. carbon dioxide as liquid were introduced into the contents of the funnel through a valve and the funnel and contents were then immersed in a water bath and cooled to 41°C The pressure within the funnel at this temperature was about 300 p.s.i.g. Two liquid layers formed in the funnel without precipitating a solid phase (precipitation xfould occur at about 39°C.) and after shaking of the funnel and contents equilibrium between phases was obtained by letting the funnel sit for five minutes. A 17 ml. sample was drawn from the lower layer through a valve in the bottom of the funnel. The sample was ejected from the funnel into a smaller sealed chamber in which pressure was released after the funnel ras again sealed. An equal volume of ethylene dichloride was added to the sample causing dissolved water to appear as a supernatant layer* After separating the layers the water layer was again washed with an equal volume of ethylene dichloride and was analyzed for halogen content by titrating with 0.1 A NO^ solution. The titration showed 0.08 percent by weight halogen calculated as NaCl in the water which was about 2 ml. in volume.

EXAMPLE VI The procedure of Example V was repeated at a water bath temperature of 55°C The water obtained from the sample withdrawn from the funnel was found to contain 0.35 percent by EXAMPLE VII The procedure of Example V was followed for obtaining a sample washing of the sample with ethylene dlchloride was omitted. After withdrawing the sample super-atmospheric pressure was not released, but the sample was cooled to about 23eC. and additional carbon dioxide was introduced as liquid until it comprised slightly in excess of 20 percent of the weight of the sample -with super atmospheric pressure being about 65Ο p.s.i.g. After shaking the sample two liquid layers formed and the more dense solvent layer was withdrawn from the sample. The remaining supernatant water layer was multiply washed with equal volumes of liquid carbon dioxide. After three washings the water was found to contain 0.03 weight percent s-trloxane and 0.05 weight percent halogen calculated as NaCl. The proportion of water in the sample was similar to that of Example V.

EXAMPLE VIII The procedure of Example V la followed except that the temperature of the funnel is adjusted to 32°C. and a total of — in 17 ml of liquid carbon dioxide is introduced/to the funnel to provide total vapor pressure of ΙΟβΟ p.s.i.g, A sample is withdrawn from the funnel and cooled to 30°C. condensing the carbon dioxide while 15 ml. additional liquid carbon dioxide is introduced to maintain the vapor pressure. After separating two phases which form in the sample and washing the water phase three successive timee with liquid carbon dioxide, the halogen content of the water is determined by titration with 0.1 N AgNO^f and is found to be less than in Example VII. 25176/2 EXAMPLE IX 70 gms. monomethyl trioxane and 3 gms. sea water are intimately mixed at 25i°C After letting the mixture sit for five minutes two phases which appear in the mixture are separated and are introduced into separate stainless steel separatory funnels.. Nitrous oxide is introduced into the contents of each of the funnels until pressures of 400 p.s. i.g. are obtained. After thorough · mixing ί of the contents the contents of each funnel separates into two phases. A sample drawn from the bottom of the funnel containing the lower phase of the initial mix'ture is washed twice'■·;··' with nitrous oxide and is analyzed for halogen by titration with 0.1 N Ag O-j. The halogen content calculated as NaCl is'' found to- be less than 0.1 weight percent of the water solution.

The procedure of Example XI may be repeated using 1 , 3 , , trioxepane or using 1 , 3 , 5 » s-trioxane, 2 , 4 , 6 , trioxy to yield results similar to that of Example XI. The mono- methyl and mono-ethyl substituents of dioxane, s-trioxane, and trioxepane may also be used with similar results, and at lower temperatures than are possible with the unsubstituted solvents, but with somewhat greater hydrolysis of the solvent.

! EXAMPLE X gms. salt water ( 1.6 percent NaCl), 40 gms. s-trioxane and gms. trioxepane at 18°C . are placed in a separatory funnel "and intimately mixed. After letting the funnel sit for five minutes the two phases which appear are separated and the lower phase fraction is mixed with an equal volume of ethylene dichloride. 25176/2 The water and solvent phases which appear are separated and the water is washed twice with equal volume of ethylene dichloride at 18°C. The halogen content calculated as NaCl is determined by titration with 0.1 N AgNQ^. Halogen content is less than 0.3 weight percent of water solution. The lower phase fraction in the separatory funnel constituted about two-thirds the original total volume, and from about 10 perceht to 15 percent of the lower phase was absorbed water.

EXAMPLE XI A process of Example X is repeated and 6 ml. of liquid carbon dioxide is introduced into the separatory funnel before mixing of the components. The extracted water is of similar volume to that of Example X, and has a halogen content calculated as HaCl of less than 0.1 weight percent of water solution.

EXAMPLE XII gms. sea water, 30 gms. tetraoxocane and 30 gms. s-trioxepane at 18°C. are placed in a separatory funnel and intimately mixed. After letting the funnel sit for five minutes the two phases which appear are separated and the lower phase fraction is thoroughly mixed with an equal volume of condensed difluorodichloromethane in a sealed stainless steel separatory funnel at 25°C. and 90 p.s.i.g. After funnel and contents sit for five minutes a sample is withdrawn from the upper phase which forms in the funnel and is washed twice with condensed difluorodichloromethane and analyzed for halogen content by titration with 0.1 H AgNO^. Calculated as HaCl the halogen content is less than 0.4 weight percent of water solution. 25176/2 Condensible gases generally and in particular members of those sold commercially as "freon" such as, for example trifluoromonochloromethane may be used as a separatory agent in the process of this invention. Water immiscible halogenated solvents are also generally suitable as separatory agents herein, The procedure of Example XII is repeated at 25°C. using meta-dioxane and s-trioxane in place of tetraoxecane and trioxepane. The halogen content calculated as NaCl is less then 0.5 weight percent of water solution.

It is possible in the processes of this invention wherein s-trioxane is used as solvent to concentrate the salinity of the rejected phase to about 8.0 percent by weight NaCl in water, and similar concentrations may be expected with other solvents herein disclosed. Synergistic solvent action may be provided by using multiple solvents in combination e.g. s-trioxane and trioxepane as shown in Example X, to yield potable water in greater quantity than can be obtained by use of either solvent alone with the given solvents, and the range of processing temperatures may be greatly increased so that sea water at ambient temperature may be processed without heating, the freezing range of th© solvent mixture being depressed by s-trioxepane which freezes at 4°C EXAMPLE XIII ml of 26 wt. percent solution of HaCl in water and 7.5 gms. s-trioxane were placed in a separatory funnel at 55°C. and stirred. A 2 ml. trioxane rich supernatant phase appeared and crystalline salt was observed in the lower phase. Upon 25176/2 cooling to 48°C. crystals of s-trioxane precipitated. Upon heating the components in a water bath at 64°C. the supernatant s-trioxane rich phase was reduced to ½ ml. or less while an estimated l ml. of NaCl crystals appeared on the bottom of the funnel. 7-_r gms. of s-trioxane were added and the temperature raised to 68°C. and the contents stirred. After allowing to stand about 2 ml. of 16a - NaCl crystals were removed from the bottom of the funnel and were washed with acetone, dried, and found to weigh 1.5 gms.

EXAMPLE/IV. . 168 gms. of s-trioxane were placed in a separatory funnel and molted at 62°C. in a water bath. . 7 cc_ of 3.5 wt. percent solution of NaCl in water were added to the funnel drop while the temperature was maintained at about 55°C_ Upon the addition of each drop of saline solution salt crystals were observed to precipitate in the funnel. The water appeared to be completely absorbed. 2 cc, of additional 3.5 wt. percent solution of NaCl in water were added with dissolution of all salt crystals in the vessel being observed and with a second liquid phase dispersed as droplets throughout the funnel content appearing. Separation of the disperse phase as a supernatant layer was not effected by standing and the density differential between phases was not sufficient to cause separation of layers until the salt rich phase was more dilute. This extraction method was considered less satisfactory than the addition of solvent to saline solution as in the preceding examples.

Precipitation and separation of phases conducted in the manner of Example II, but at increasing pressures to 1500 p.s.i. g. did not materially affect phase volumes, and phase compositions were found to be similar to those of Example II in NaCl content.

As used herein "oxa-cyclic" means cyclic organic compounds consisting of carbon and oxygen as cyclic members, and all other nomenclature is as prescribed in Nomenclature of Organic Chemist y 1957* Scientific Publications, London, 1958 which embodies approved nomenclature of the International Union of e a A lied hemistr a.

Physical and chemical data for ox -cyclic compounds including preparation are given in Formaldehyde, Walker 3rd Ed. Reinhold Publishing Co., Inc., New York, 1964.

While certain examples have been described for the purpose of illustrating the invention,, it is to be understood that variations will be suggested to persons familiar in the art and that the invention is not limited by the examples illustrated. - 19 - 25176/3

Claims (6)

1. A process for purifying an impure aqueous solution comprising the steps of contacting, preferably multiple times, under conditions to effect incomplete miscibility therewith and formation of plural phases, a quantity of at least one oxacyclic solvent with molecular cyclic configured portion comprising (-C-0-C-) etheral bonds, optionally with additional contacting with condensable gas not exceeding about 20 by weight of solution, one of which phases formed comprising a lower proportion of said impure content with respect to water content therein than that in said aqueous solutionbelng purified, separating the phases, contacting preferably multiple times said one phase comprising a lower proportion of impure content with at least one agent either to form an azeotrope or to form separate phases of water and oxacyclic solvent therefrom, and then distilling said azeotrope or separating said water and oxacyclic solvent phases and preferably evaporating said gav, if present, to provide purified water.

2. A process for reducing the saline content of an aqueous solution containing more than about 1.6 percent by weight mineral salt comprising the steps of contacting, preferably multiple times, under conditions to effect incomplete miscibility therewith and formation of plural phases a quantity of at least one oxacyclic solvent compound with molecular cyclic configured portion comprising (-C-0-C-) ether bonds, optionally with additional contacting with a condensable gas not exceeding about 20 percent by weight of solvent, one of which plural phases formed ie a solvent-water phase comprising water of reduced salinity, separating the phases formed and removing said oxacyclic compound to provide - 20 - 25176/3 water of reduced salinity and to provide liquid and/or solid of high salinity.

3. The process of Claim 1 or 2, wherein removal of said oxacyclic compound is effected by dissolved or condensed condensable gas being contacted with said one phase to increase the content of dissolved and condensed gas in said phase.

4. The process of Claim 1 or 2, wherein one of said plural phases is in the solid state.

5. The process of Claim 1 or 2, wherein said oxacyclic solvent is one or a mixture of para-dioxane, meta-dioxane, dioxo lane, dioxepane, o-trioxane, tetra-oxocane, and monomethyl and dimethyl and monoethyl and diethyl substituent derivatives of any of the foregoing and substituted derivatives comprising a co bination of the foregoing substituents.

6. The process of Claim 1 or 2, wherein said oxacyclic solvent is one or a mixture of s-trioxane, trioxepane, tetra-oxocane, and monomethyl and monoethyl substituent derivatives of any of the foregoing and substituted derivatives comprising a combination of the foregoing substituents. 7· The process of Claim 1 or 2, wherein said condensable gas or said agent comprises sulfur dioxide, nitrous oxide, fluorinated methane or ethane, or preferably carbon dioxide. 8· The process for purifying a solution substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings. For the Applicants DR. RSU [JSnHjOOLLDD^A ΟγHΗNΝjiAAi;TD PARTNERS By: